The invention relates generally to systems and methods for determining the physical characteristics of objects and, more particularly, to optical systems and methods for determining surface characteristics and reflective or refractive characteristics of reflective, transparent or translucent objects.
Due to ever increasing needs for environmentally safe energy, various solar power systems are currently being examined and/or developed with a view towards their implementation as a viable alternative to current energy production systems. One of the primary methods being considered for achieving high efficiency solar power on earth or in space is the use of reflective surfaces, ranging in size from 3.times.4 feet to 30.times.40 feet, to concentrate or focus sunlight onto an area where it is converted to electrical or thermal energy for process heating, space heating, and the like. The use of such reflective surfaces requires the measurement of detailed optical reflective characteristics thereof. In particular, the surface waviness from a very low frequency (i.e., slope error measurements that occur on the order of a few inches) to a very high frequency (i.e., specular and non-specular slope error measurements that occur over fractions of an inch) must be measured in order to ensure that the system will meet the focusing requirement and redirect the solar energy with minimal loss due to scattering of the light out of the cone angle required by the system.
A prior art method for assessing the specularity of a reflective surface includes the projection of a beam of light onto a part of the surface and subsequent measurement of the amount of energy reflected back onto a detector. In some such methods, the total reflectivity is determined over a certain cone angle, for example, 10 or 20 milliradians, and reflectivity is then reported as a function of the cone angle. Other such prior art methods utilize integrating spheres to determine both the total hemispherical reflectivity and the reflectivity relative to a particular cone angle by blocking the incident light over a specified angle and subtracting this value from the total reflectivity value. The difference obtained is the specular reflectivity.
Another prior art method for assessing the specularity of a reflective surface involves the projection of a laser beam onto a surface and measurement of the reflected beam position. The surface angle is calculated by utilizing the beam position measurement result. However, since an extremely fine laser beam is required to determine specularity and hundreds or thousands of data points are required for producing a statistically valid result, such prior art methods are very time consuming.
Generally, these prior art methods do not provide data on the microstructure of the surface such as the mean and standard deviation of surface waviness and do not actually measure the angles of the surface or radius of curvature, especially over very small (microscopic) distances for the entire surface. Therefore, they are of limited usefulness not only in correlating optical performance to the fabrication technique used in producing the mirror or other object which is being examined but also in correlating optical performance to environmental conditions. Consequently, they are also of limited usefulness in assessing how such factors determine or affect the surface quality.
A system for measuring the physical characteristics of reflective and refractive objects and materials is thus needed that is capable of measuring the actual surface slope angle of reflective surfaces over virtually an entire surface and the refractive characteristics of an entire refractive object. Such a measuring system is also needed that can provide measurements of surface waviness (standard deviation of slope error) as well as reflectivity, refractivity, radius of curvature, local or global cant angles and surface slope angles and surface degradation at any given point or points very rapidly and with a high degree of accuracy.
A measuring system is also needed that can provide such capabilities without utilizing moving parts that can wear, break or become misaligned because of vibration, shock or wear. In addition, a measuring system is needed that can provide such capabilities without being affected by light or other radiation from extraneous sources or from extraneous reflections. Further, a measuring system is needed in which components thereof can be interfaced with computer hardware and software so as to analyze and provide data in appropriate formats for evaluation.
Accordingly, a principal object of the present invention is to provide a surface characteristics measuring system and method for reflective surfaces which provide a high degree of accuracy.
It is another object of the present invention to provide a surface characteristics measuring system and method for reflective surfaces which provide a high degree of accuracy in microscopic examination of the surfaces.
It is another object of the present invention to provide a refractive characteristics measuring system and method for transparent or translucent objects which provide a high degree of accuracy.
It is another object of the present invention to provide a refractive characteristics measuring system and method for transparent or translucent objects which provide a high degree of accuracy in microscopic examination of the objects.
It is also another object of the present invention to provide a physical characteristics measuring system and method for reflective and refractive objects which are capable of rapidly providing the desired measurements.
It is also another object of the present invention to provide a physical characteristics measuring system and method which have minimal moving parts for enhanced reliability and longevity.
It is another object of the present invention to provide a physical characteristics measuring system and method in which the component structures thereof are relatively simple in construction for enhanced reliability and longevity.
It is still another object of the present invention to provide a physical characteristics measuring system and method which are not significantly affected by extraneous radiation.
It is another object of the present invention to provide a physical characteristics measuring system and method having appropriate computer hardware and software for control of data acquisition, analysis, storage and presentation.
It is also an object of the present invention to provide a physical characteristics measuring system and method in which the component structures thereof are relatively light-weight, rugged and compact to facilitate use thereof.